(1) Field of the Invention
The present disclosure relates to a solar cell.
(2) Description of Related Art
FIG. 7 shows a solar cell disclosed in Patent Literature 1 (Japanese Patent Laid-Open Publication No. 2008-124381). This solar cell comprises a solar cell element 11 and an optical lens L. The solar cell element 11 comprises a p-type GaAs buffer layer 13a, a p-type InGaP-BSF layer 13b, a p-type GaAs base layer 13c, an n-type GaAs emitter layer 13d, an n-type InGaP window layer 13e, and an anti-reflection layer 15. These layers 13a-15 are stacked in this order on a semiconductor substrate 12.
The n-type InGaP window layer 13e is irradiated with sunlight which passes through the optical lens L and the anti-reflection layer 15. This irradiation of sunlight generates an electric power.
FIG. 8 shows a solar cell element disclosed in Patent Literature 2 (Japanese Patent Laid-Open Publication No. 2010-010704). This solar cell element comprises a top cell T formed of InGaP, a middle cell formed of GaAs, and a bottom cell formed of InGaAs. These three cells T, M, and B are electrically connected through tunnel junction layers 5-8. The top cell T, the middle cell M, and the bottom cell B absorb lights having a different wavelength from each other to generate an electric power. For this reason, this solar cell element has high photoelectric conversion efficiency.